Despite more than 30 years of study, the brain renin-angiotensin system (RAS) continues to defy explanation. Our lack of understanding of how the brain RAS is organized at the cellular and regional levels has made it difficult to resolve long-sought questions of how angiotensin II (AngII) is produced in the brain, and the precise mechanisms by which it exerts its actions. A major reason for this is the difficulty in experimentally dissecting the brain RAS- at the regional, cellular and whole organism levels. During the last funding period we have developed an array of genetic tools to cell- and site-selectively manipulate the murine brain RAS in vivo. Furthermore, we have established state-of-the-art technology for long-term analysis of blood pressure and volume homeostasis in conscious mice. Harnessing the power of a combination of these new tools, we will dissect the regional, cellular (neurons vs. glia) and functional significance of the brain RAS in the context of both physiological and pathophysiological states. Focusing on critical cardiovascular regulatory centers, including subfornical organ coupled networks involved in vasopressin release and sympathetic outflow, we will determine precise mechanisms of brain AngII production and action in these pathways. We will also begin to further explore a potentially exciting new central AngII signaling mechanism involving reactive oxygen species. We believe these studies have the potential to clarify the basic biology of the brain RAS, and impact our understanding of how this system regulates cardiovascular and fluid balance in normal and disease states.